1. Field of the Invention
The present invention relates to a method and system for controlling the toner concentration in a developer for developing an electrostatic latent image, and in particular, to a toner concentration control method and system for use in electrophotographic copying machines.
2. Description of the Prior Art
In an electrophotographic copying machine employing the so-called two component developer comprised of toner and carrier beads, it has been known to control the concentration of toner in the developer. One approach to detect the toner concentration of developer relies on a variation in inductance depending on the toner concentration, and another approach is to detect the optical density of a reference pattern formed on a photosensitive drum. Conventionally, the toner concentration was measured by either of these approaches and the thus measured toner concentration was compared with a predetermined reference level at a predetermined interval, and when the measured toner concentration was found to be lower than the reference level, a toner replenishing unit was activated to supply a predetermined amount of toner to the developer.
In this manner, in accordance with the prior art technique, a predetermined amount of toner was replenished every time when the measured toner concentration was found to be lower than the reference level, so that the developer could be prevented from becoming toner scarce condition. However, in accordance with such prior art approach, since the developer was examined at regular intervals as to whether or not its toner concentration was lower than the reference level irrespective of the degree of toner concentration, data processing was carried out unnecessarily, which was a burden to a control unit. Besides, since a predetermined amount of toner was replenished irrespective of the degree of deviation of the detected toner concentration from the reference level, it was often observed that the toner concentration became excessive or too scarce, which thus caused instability in the performance of development.